1. Field of the Invention
The present invention relates to the manufacturing of semiconductor devices or the like. More particularly, the present invention relates to the dispensing of photoresist onto a wafer or other substrate.
2. Description of the Related Art
In general, the manufacturing of semiconductor devices involves subjecting a wafer to a series of processes such as diffusion, photolithography, etching, ion implantation and deposition processes. In particular, the photolithography and etching processes are carried out to form a pattern, e.g., a circuit pattern, on the wafer. The photolithography process entails forming a mask on a wafer to expose portions of a layer underlying the mask. The etching process entails removing the portions of the layer exposed by the mask.
The photolithography process begins by dispensing a chemical, namely a photoresist, onto a surface on a wafer, and forming a uniform thin layer of the photoresist over the entire surface. The layer of photoresist is then exposed by light directed through a reticle. The reticle has a pattern corresponding to the pattern to be formed on the wafer. Accordingly, an image of the pattern of the reticle is transferred to the layer of photoresist. Then, the layer of photoresist is developed. The developing process removes either the exposed or non-exposed portions of the photoresist to thereby form a photoresist pattern, i.e., a mask, on the wafer.
FIG. 1 illustrates a conventional photoresist dispensing apparatus of semiconductor device manufacturing equipment.
As shown in FIG. 1, the dispensing apparatus includes bottles 10 containing photoresist, a supply line 20 connected to the bottles 10, a pump 30 and a filter 40 disposed in the supply line 20, and a spray nozzle 50 connected to an end of the supply line 20. The photoresist is withdrawn from the bottles 10 and is forced through the supply line 20 by the pump 30. Then, the photoresist is sprayed onto a wafer W by the spray nozzle 50. The most important aspect of spraying the photoresist onto the wafer W is that the photoresist cover the wafer W uniformly.
However, even if the layer of photoresist covering the wafer W has a uniform thickness, the photomask formed from the layer of photoresist will be defective if the photoresist itself contains foreign substances. A defective photomask will, in turn, cause defects in the pattern formed on the wafer by the subsequent etching process. In view of this, the filter 40 is disposed in the supply line 20 to remove foreign substances from the photoresist before the photoresist is dispensed onto the wafer W.
Furthermore, bubbles generated in the photoresist flowing through the supply line 20 affect the quantity of photoresist sprayed by the nozzle 50. Accordingly, bubbles in the photoresist can cause defects in the mask and hence, in the pattern formed by the etching process. In fact, even micro-bubbles entrained in the photoresist can severely influence the quality of a pattern formed according to the design rule of today's highly integrated semiconductor devices. Therefore, the filter 40 is also designed to remove bubbles from the photoresist in the supply line 20.
However, the bubbles removed form the photoresist by the filter 40 form a film that floats on the liquid in the filter 40. The film acts as a load on the photoresist flowing through the filter 40. Thus, the rate at which the photoresist passes through the filter 40 rapidly decreases as bubbles and foreign substances are simultaneously filtered. That is, the bubbles offer resistance to the photoresist passing through the filter 40, thereby reducing the volume of photoresist sprayed through the nozzle 50.
Also, the pressure generated at the inlet of the dispensing pump 30, which acts to withdraw photoresist from a bottle 10, becomes weaker than the pressure generated by the dispensing pump 30 at its outlet to force photoresist through the nozzle 50. The effect of this pressure difference manifests itself along the entire length of the supply line 20 from the bottles 10 to the dispensing pump 30. Consequently, even more bubbles are created in the photoresist flowing through the supply line 20. In fact, the problem can exacerbate until an entire portion of the supply line 20 is occupied by bubbles, i.e., a gap that is devoid of photoresist may be produced in the supply line 20. Thus, the rate at which the photoresist sprayed through the spraying nozzle 50 fluctuates and, as a result, the thickness of the layer of photoresist covering the wafer is not uniform. As mentioned above, the end results are a defective mask, and defects in the pattern formed on the wafer by an etching process that uses the mask.